// Mutual exclusion spin locks.

//
#include <types.h>
//
//
#include <defs.h>
//
#include <param.h>
//
#include <x86.h>
//
#include <memlayout.h>
//
#include <mmu.h>
//
#include <proc.h>
//
#include <spinlock.h>
//初始化锁
void initlock(struct spinlock *lk, char *name) {
	lk->name = name;
	lk->locked = 0;
	lk->cpu = 0;
}

// Acquire the lock.
// Loops (spins) until the lock is acquired.
// Holding a lock for a long time may cause
// other CPUs to waste time spinning to acquire it.
void acquire(struct spinlock *lk) {
	pushcli();	// disable interrupts to avoid deadlock.
	if (holding(lk))
		panic("acquire");

	// The xchg is atomic.
	while (xchg(&lk->locked, 1) != 0)  //xchg指令完成testset
		;

	// Tell the C compiler and the processor to not move loads or stores
	// past this point, to ensure that the critical section's memory
	// references happen after the lock is acquired.
	__sync_synchronize();

	// Record info about lock acquisition for debugging.
	lk->cpu = currentcpu();
	getcallerpcs(&lk, lk->pcs);
}

// Release the lock.
void release(struct spinlock *lk) {
	if (!holding(lk))
		panic("release");

	lk->pcs[0] = 0;
	lk->cpu = 0;

	// Tell the C compiler and the processor to not move loads or stores
	// past this point, to ensure that all the stores in the critical
	// section are visible to other cores before the lock is released.
	// Both the C compiler and the hardware may re-order loads and
	// stores; __sync_synchronize() tells them both not to.
	__sync_synchronize();

	// Release the lock, equivalent to lk->locked = 0.
	// This code can't use a C assignment, since it might
	// not be atomic. A real OS would use C atomics here.
	asm volatile("movl $0, %0"
				 : "+m"(lk->locked)
				 :);

	popcli();
}

// Record the current call stack in pcs[] by following the %ebp chain.
void getcallerpcs(void *v, uint pcs[]) {
	uint *ebp;
	int i;

	ebp = (uint *)v - 2;
	for (i = 0; i < 10; i++) {
		if (ebp == 0 || ebp < (uint *)KERNBASE || ebp == (uint *)0xffffffff)
			break;
		pcs[i] = ebp[1];	   // saved %eip
		ebp = (uint *)ebp[0];  // saved %ebp
	}
	for (; i < 10; i++)
		pcs[i] = 0;
}

// Check whether this cpu is holding the lock.
int holding(struct spinlock *lock) {
	int r;
	pushcli();
	r = lock->locked && lock->cpu == currentcpu();
	popcli();
	return r;
}

// Pushcli/popcli are like cli/sti except that they are matched:
// it takes two popcli to undo two pushcli.  Also, if interrupts
// are off, then pushcli, popcli leaves them off.

void pushcli(void) {
	int eflags;

	eflags = readeflags();
	cli();
	if (currentcpu()->ncli == 0)
		currentcpu()->intena = eflags & FL_IF;
	currentcpu()->ncli += 1;
}

void popcli(void) {
	if (readeflags() & FL_IF)
		panic("popcli - interruptible");
	if (--currentcpu()->ncli < 0)
		panic("popcli");
	if (currentcpu()->ncli == 0 && currentcpu()->intena)
		sti();
}
